The present invention relates to fiber-forming polymers and more particularly to a fiber-forming copolyamide having hexamethylene adipamide units and a minor portion of 2-methyl-pentamethylene adipamide units and fibers produced therefrom.
Nylon yarns are used in a wide variety of knit and woven fabrics for upholstery, swimwear, lingerie, hosiery and outerwear and in yarns used for carpeting. Most nylon yarns are spun from one of the two commonly used nylon polymers, poly(hexamethylene adipamide), referred to as nylon 66 and poly(.epsilon.-caproamide) referred to as nylon 6. While both polymers can be used for most types of textile yarns, the choice of either nylon 66 or nylon 6 is known to impart advantageous or disadvantageous properties to the yarns depending on the end use. However, for most nylon producers, it is not economically feasible to include products made from both types of polymer in their product line to accommodate end use needs.
While nylon 66 has a number of inherent advantages, nylon 66 producers recognize that nylon 66 is not as readily dyeable as nylon 6, especially with large bulky dye molecules such as those of pre-metalized and non-leveling acid dye classes. To increase dyeability, the salt used to make nylon 66, hexamethylene diammonium diadipate, has been copolymerized with 0.2 to 5% of .omega.-aminocarboxylic acids having 4 or about 6-12 carbon such as .epsilon.-caprolactam as disclosed in U.S. Pat. No. 3,707,522 so that the resulting copolymer is primarily nylon 66 with some other monomer such as .epsilon.-caproamide (6 nylon) monomer. For convenience, the copolyamide containing .epsilon.-caproamide will be referred to hereinafter as nylon 66/6.
One problem with nylon 66/6 fibers is that the copolymer contains unreacted .epsilon.-caprolactam monomer and some cyclic oligomer. Without water extraction of the polymer, prolonged spinning of nylon 66/6 with as little as 1.5% .epsilon.-caproamide produces monomer and oligomer which sublime onto the face of the spinneret requiring it to be wiped frequently. Consequently, continuity of the spinning is disrupted for "wiping" and the size of the yarn packages may be limited. Also, in feed yarns for texturing containing nylon 66/6, or in high RV, high speed spun yarns containing either homopolymer nylon 66 or nylon 66/6, monomer and oligomers continue to migrate from the interior to the surface of the yarn over time. Thus, the frictional properties of the yarn can change with aging which can cause an erratic response in texturing and deposits can be formed on the texturer's equipment requiring that frequent cleaning be performed. Moreover, nylon 66/6 fibers do not crystallize as readily as the homopolymer nylon 66, and as a result, are more difficult to stabilize in a fabric during heat setting.
While other monomers such as polyethers have been copolymerized with polyhexamethylene adipamide to improve dye receptivity, such fibers are not as white or as heat stable as those of 100% nylon 66 and therefore are often unsuitable for apparel textile uses.